1. Field of the Invention
The present invention relates to method of extraction of juice from fruits or vegetables, and more particularly to the use of a screw press having a gradual and continuous slope of the body of the feed screw for such extraction.
2. Description of the Prior Art
Screw presses have been widely used for the extraction of liquids from solids or semi-solids in the food industry. A primary application of such presses is the grape and wine industry. It is common practice to introduce harvested grapes into a destemmer or precrusher which serves to free the grapes from their stems. The destemmer in operation causes rupture damage to a large proportion of the incoming fruit which results in a free run of juice in the mass of grapes, or must, as the mass is termed. Before pressing the must to remove the remainder of the juice from the grapes, the must is predrained of this free running juice. Several methods are in common use. For example, the must containing the free run juice is transferred from the destemmer to settling tanks, where the free run juice is allowed to settle out. A typical settling time may be on the order of two hours. After settling, the free juice is drawn off and carried to a separator to remove solids which have collected from the crushing or destemming operation. The remaining must is dumped into feed troughs for transport to the final pressing operation. A typical time for the dumping and feeding operation may be on the order of one-half hour. The must delivered to the final press still contains free run juice since the settling tank cannot completely drain the original must in the alloted time. The extreme wetness of the must often causes difficulty in the conveyors and other predrainers which may be utilized prior to the final pressing.
Other systems utilize drag screens disposed along the conveyors from the destemmer to the presses which allow the free run juice to drain off and be collected in drain pans beneath the conveyors. This approach is also slow since the transport time must be long to provide sufficient draining time. Even with predraining, the wet must delivered to the presses causes difficulty in feeding due to slippage of the wet mass of grapes. This problem varies with the type of grapes being handled.
In the wine industry, great effort is expended to get a crop harvested at the proper time, with pickers working night and day until harvesting is complete. However, when trucks carrying the harvested crop arrive at the winery, it is common to have long waiting periods for unloading. This delay is generally due to the long times required for predraining and conveying of the must after destemming. Thus, the throughput of the winery is essentially limited by this operation.
Attempts have been made in the past to reduce the predrain time and to deliver a much dryer must to the final press. For example, U.S. Pat. No. 4,117,776 to Hunt describes a screw press apparatus having a two-section press. The first section receives the must directly from the destemmer without requiring settling tanks, drag screens, or the like. The feed screw of the first section includes a segmented body having a straight section, a sharply tapered section and a final straight section. Must is introduced into the first flights of the feed screw and carried along to the tapered body, thereby reducing the volume of the must producing a squeezing action. Further draining is then accomplished in the final straight section. The feed screw operates within a conventional chamber or cage formed from filter screens such that the free run juice squeezed from the must passes through the screens and is collected. The speed of rotation of the feed screw is adjustable in the order of 50 to 300 rpm. After the predraining operation, the resulting pulp is passed directly to the second section of the apparatus which operates as a conventional screw press compressing the predrained must to a final dry cake. The screw feed for the second section of the apparatus is separately rotated and designed to rotate on the order of 10 to 50 rpm. Although an improvement over the prior art and useful for many applications, in predraining grapes and pressing grapes, a number of problems have been found. First, the extremely wet undrained must, when introduced into the inlet of the predrainer section of the apparatus, caused slippage between the mass of grapes and the spiraling feed screw. Next, the relatively acute taper of the feed screw body contributed further to the slippage and caused difficulty in controlling the percentages of juices obtained in the predraining phase. Difficulty has also been encountered in attempting to independently adjust the rotational speeds of the feed screw in the predrainer section and in the press section to obtain optimum throughput. Another difficulty in the predrainer section involves the cleaning of the filter screens which requires excessive time and labor. In accordance with the present invention, the difficulties encountered in the predrainer of the previous Hunt patent have been solved, and a screw press provided which operates as a high speed predrainer for grapes and the like.
In addition to the wine and grape industry, many products require dewatering at certain stages in processing. Examples are: sugar beets; kelp; vegetables; spent grains; citrus pulps; pineapple peels; industrial sludges; animal stomachs; alfalfa; plastics; and cranberries. Many of these are wastes from food processing and the like to be completely dried and utilized for animal feeds. Such drying commonly requires high BTU burners which use large amounts of energy. Efficient screw presses, in accordance with the present invention, can predrain or remove a large percentage of liquids from such products quickly and at low cost. Thus, the energy requirements for final drying are greatly reduced.
Screw presses and other types of presses available in the prior art often use star wheels or breaker bars to mascerate grape skins and seeds, imparting a "grassy" taste to the juice or wine. When such presses are used with tobacco or paper sludges, these devices cause hard spots in the finished product called "fish eyes". Our invention advantageously dispenses with the need for star wheels or breaker bars.